Conventionally, a construction machine such as an excavator having an upper rotary body is arranged so that the rotary body rotates with respect to its frame via a swing circle.
In these days, there has been developed a hybrid electric rotary excavator in which a rotary body is driven not by a hydraulic motor but by an electric motor, and work machines and a base carrier are driven by a hydraulic actuator (refer to, for example, Patent Document 1)
In such an electric rotary excavator, rotation of the rotary body is driven by the electric motor. Therefore, even when the rotary body is rotated along with a raising operation of hydraulically driven boom and arm, the rotation of the rotary body is not affected by the raising operation of the boom and arm. Therefore, compared to the case where the rotary body is also hydraulically driven, a loss in control valves and the like can be reduced, resulting in satisfactory energy efficiency.
[Patent Document 1] Japanese Patent Laid-Open Publication No. 2001-11897